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Geology Exam 2, Lecture 11 Ch 9
Geology
14
Geology
Undergraduate 1
03/16/2010

Additional Geology Flashcards

 


 

Cards

Term

What distinguishes the two different eruptive styles.  

Definition

Effusive Eruptions

- Produce mainly lava flows, low viscosity basaltic lava

- Mid-ocean Ridges & Oceanic Hotspots

-        

Explosive (pyroclastic) eruptions

- Produce clouds and avalanches of pyroclastic debris.  Occurs when gas expands in the rising magma but cant escape

- Subduction zones

Term

The definition of viscosity.  

Definition

Viscosity – fluid’s resistance to flow

            -High viscosity – doesn’t flow easily (maple syrup in fridge)

            -Low viscosity – flows easily (heated maple syrup)

1.  Temperature UP, viscosity DOWN

2.  Silica content SiO2 UP, viscosity UP

Term

The relative viscosity of the three main types of igneous magma.  

Definition

Basalt - LOW Si, LOW viscosity -flows

Andesite – between

Rhyolite - HIGH Si HIGH viscosity –doesn’t flow as well

Term

The type of eruption produced by low viscosity magma and high viscosity magma. 

Definition

Basalt - LOW viscosity – effusive eruptions

 

Rhyolite - HIGH viscosity – explosive eruption

Term

The difference between a pahoehoe flow, aa flow, and lava tube.  

Definition

Pahoehoe lava flow

-Basaltic lava that freezes into smooth, glassy, rope-like ridges

 

aa flow

-The surface layer of the lava freezes then breaks up due to the continued movement of lava underneath

-chunky

 

lava tube

The empty space left when a lava tunnel drains – when the surface of a lava flow solidifies while the inner part continues to flow

Term

Hazards of lava flows. 

 

Definition

·      Basaltic lava from effusive eruptions is the greatest threat


·      Lava flows can bury roads, housing developments, and cars


·      Before the lava even touches it, the building may burst into flames from the intense heat


·      Forests, orchards and fields can burn and then be buried by rock and replaced by blackness

 

Term

A couple ways to mitigate those hazards.  

 

Definition

 

-Danger assessment maps – map out the areas in the path of potential lava flows, lahars, debris flows, or pyroclastic flows

 

Evactuation – but exact times cannot be predicted

 

Diverting flows – using explosives, building dams, creating barriers etc…

 

Pumping Sea Water - May slow it down

 

Term

What causes an eruption to be explosive?  

Definition

Effect of viscosity

-High-viscosity lava (andesitic and rhyolitic) lava can clog up a volcano’s plumbing causing a build up of pressure --

 

Effect of gas pressure

-The presence of gas in the magma increases the pressure because gas expands greatly as it rises toward the Earth’s surface.

-In basaltic magma (runny) – gas bubbles rise to surface and pop causing lava to fountain in sky

-In andesitic or rhyolitic magma (viscuous) – The gas bubbles can’t escape.  The gas bubbles expand and eventually shatter the partially solidified magma creating a pyroclastic eruption

Term

The role of dissolved gasses in the magma. 

Definition

Effect of gas pressure

-The presence of gas in the magma increases the pressure because gas expands greatly as it rises toward the Earth’s surface.

-In basaltic magma (runny) – gas bubbles rise to surface and pop causing lava to fountain in sky

-In andesitic or rhyolitic magma (viscuous) – The gas bubbles can’t escape.  The gas bubbles expand and eventually shatter the partially solidified magma creating a pyroclastic eruption

Term

Hazards related to stratovolcanoes, including ash fallout, pyroclastic flows, and lahars.  

 

Definition

Ash fallout :

·      Falling pyroclasts

·      Collapsed buildings

·      Health hazards

·      Damage to machinery

·      Damage to vegetation

Pyroclastic Flow

·      Very hot, very fast, very dangerous

·      So hot and poisonous that it means instant death to anyone caught in its path

·      Because it moves so fast, the force of its impact can flatten buildings and forests

Ash Clouds:

·      Plumels travel long distances because of the wind

·      Damage to aircrafts

-Lahars – Volcanic ash and debris mix with water, causing mudflows

 

Term

Vesuvius 

Definition

-In 79AD

-Stratovolcano at a convergent boundary

-Pompeii buried in ash and pumice

Term

Nevado Del Ruiz 

Definition

-Stratovolcano

-In 1985

-Columbia

-The volcano, which took 25,000, lives in mudflows, 13 November 1985

-Could have been prevented

Term
Lava dome
Definition

Rhyolitic lava (most viscous, highest silica, coolest) when it erupts accumulates above the eruption vent forming a dome

Term
Tephra
Definition

– loose accumulation of pyroclastic grains

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